Method for concealing dark defect in image sensor

ABSTRACT

Disclosed is a method for concealing a dark defect in an image sensor. The method includes the steps of: setting a window including five sequential pixels from pixel data sequentially outputted, the third pixel and the fifth pixels being identical in Bayer color with each other and the second and the fourth pixels being identical in Bayer color with each other; calculating an average value α of the first and the fifth pixels and a plurality of α/n obtained by dividing the average value α by n; selecting one of the plurality of α/n; comparing a threshold value α+α/n calculated by adding the average value α to the selected α/n with a value of the third pixel in size; and omitting a concealment of the dark defect when the threshold value α+α/n is greater than the value of the third pixel.

FIELD OF THE INVENTION

The present invention relates to a method for concealing a dark defect in an image sensor; and more particularly, to a method for concealing a dark defect capable of being actively applied according to a pixel data.

DESCRIPTION OF RELATED ARTS

An image sensor is a device printing images by using a characteristic a semiconductor reacts to a light. That is, the image sensor is a device that a pixel detects a brightness and a wavelength of each different light coming from each different subject and reads the light in an electrical value. The image sensor plays a role in making this electrical value to a level capable of performing a signal processing.

Recently, a complementary metal oxide semiconductor (CMOS) image sensor having an excellent productivity due to a high scale of integration and a low consuming voltage has been more highlighted compared with a conventional solid camera device, i.e., a charge coupled device (CCD).

Meanwhile, a poor characteristic of the image sensor is a light signal reproduction in a low illuminated environment. It is because of an influence by a noise signal caused by a unique characteristic of the semiconductor device. This noise component degrades a ratio of a signal to a noise (SNR), thereby deteriorating an image quality.

Especially, in the low illuminated environment which the light signal is weakly entered to, an internal area should be increased, thereby increasing a signal composition entering. At this time, the noise composition is also increased with the same ratio and thus, a noise defect such as a spot is generated. Accordingly, it is called a dark defect.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a method for concealing a dark defect generating a noise defect such as a spot prominently appeared in a low illuminated environment.

In accordance with one aspect of the present invention, there is provided a method for concealing a dark defect in an image sensor, including the steps of: setting a window including five sequential pixels, e.g., a first pixel P₁, a second pixel P₂, a third pixel P₃, a fourth P₄ and a fifth pixel P₅, from a plurality of pixel data sequentially outputted, the third pixel and the fifth pixels P₃ and P₅ being identical in Bayer color with each other and the second and the fourth pixels P₂ and P₄ being identical in Bayer color with each other; calculating an average value ‘α’ of the first and the fifth pixels P₁ and P₅ and a plurality of ‘α/n’ obtained by dividing the average value ‘α’ by ‘n’, ‘n’ being a multiple of 2; selecting one of the plurality of ‘α/n’; comparing a threshold value ‘α+α/n’ calculated by adding the average value ‘α’ to the selected ‘α/n’ with a value of the third pixel P₃ in size; and omitting a concealment of the dark defect when the threshold value ‘α+α/n’ is greater than the value of the third pixel P₃.

In accordance with another aspect of the present invention, there is provided a method for concealing a dark defect in an image sensor, including the steps of: extracting a window including five sequential pixels, e.g., a first pixel P₁, a second pixel P₂, a third pixel P₃, a fourth P₄ and a fifth pixel P₅, from a plurality of pixel data sequentially outputted, the third and the fifth pixels P₃ and P₅ being identical in Bayer color with each other and the second and the fourth pixels P₂ and P₄ being identical Bayer color with each other; calculating an average value ‘α’ of the first and the fifth pixels P₁ and P₅ and a plurality of ‘α/n’ obtained by dividing the average value ‘α’ by ‘n’, ‘n’ being a multiple of 2; selecting one of the plurality of ‘α/n’; comparing a threshold value ‘α+α/n’ calculated by adding the average value ‘α’ to the selected ‘α/n’ with a value of the third pixel P₃ in size; judging an existence of an edge within the window by using the comparison result; and performing the concealment of the dark defect when the comparison result is affirmative.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become better understood with respect to the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:

FIG. 1 is a flowchart schematizing a method for concealing a dark defect in accordance with the present invention;

FIG. 2 is a diagram for explaining an arrangement of pixels of a mosaic structure and a data format in accordance with the present invention;

FIG. 3 is a diagram illustrating a window installed in the pixel data outputted in a series of sequential orders illustrated in FIG. 2;

FIG. 4 is a graph illustrating a dark defect discriminating region by using an average value ‘α’ and a threshold value ‘α+α/n’ in accordance with the present invention;

FIG. 5 is a diagram illustrating an embodiment of detecting a dark defect within an installed window in accordance with the present invention;

FIG. 6 is a diagram illustrating an embodiment showing an edge existing within an installed window in accordance with the present invention;

FIG. 7 is a diagram illustrating an edge discriminating zone; and

FIGS. 8A and 8B are photographs of transmission electron microscopy (TEM) illustrating an image quality improvement of an image sensor in case of applying a method for concealing a dark defect in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, detailed descriptions on preferred embodiments of the present invention will be provided with reference to the accompanying drawings.

FIG. 1 is a flowchart schematizing a method for concealing a dark defect in accordance with the present invention and FIG. 2 is a diagram for explaining an arrangement of pixels of a mosaic structure and a data format in accordance with the present invention.

With references to FIGS. 1 and 2, a method for concealing a dark defect in accordance with the embodiment of the present invention will be examined. Hereinafter, reference denotations, G, B and R denote a green color, a blue color and a red color, respectively.

The arrangement of the pixels uses a mosaic arrangement method illustrated in FIG. 2 and the pixel data are outputted in a series of sequential orders of GRGRGRGR and BGBGBGBGBG at two rows A and B.

FIG. 3 is a diagram illustrating a window installed in the pixel data outputted in the series of sequential orders illustrated in FIG. 2.

As a first step of the method for concealing the dark defect, a window (W) comprised of five sequential pixels from a plurality of pixel data sequentially outputted, i.e., a plurality of pixel data of a first pixel P₁ indicating B, a second pixel P₂ indicating G, a third pixel P₃ indicating B, a fourth pixel P₄ indicating G and a fifth pixel P₅ indicating B of the B row in FIG. 2, is set at step S101. Herein, a present pixel subjected to a dark defect discrimination among the first pixel P₁, the second pixel P₂, the third pixel P₃, the fourth pixel P₄ and the fifth pixel P₅ is the third pixel P₃ indicating B. The third pixel P₃ is placed in the right center N.

The first pixel P₁, the third pixel P₃ and the fifth pixel P₅ have Bayer color of B. The second pixel P₂ and the fourth pixel P₄ have Bayer color of G. Meanwhile, the window (W) can be simply formed by using five shift resistors. Concealment of the dark defect is first performed to the third pixel P₃ and then, the concealment of the dark defect is performed to the fourth pixel P₄ indicating G placed next to the center N+1.

In the installed window (W), an average value ‘α’ is calculated by using the first pixel P₁ and the fifth pixel P₅ having the Bayer color of B identical with the Bayer color of the third pixel P₃ and a plurality of ‘α/n’ are calculated by the average value ‘α’ divided by ‘n’ that is a multiple of 2 at step S102.

Herein, the average value ‘α’ is the average value of the first pixel P₁ and the fifth pixel P₅ so that the average value can be denoted with a condition of (P₁+P₅)/2. At this time, values denoted with the first pixel P₁ and the fifth pixel P₅ are codes, i.e., voltages, corresponding to the values of the first pixel P₁ and the fifth pixel P₅ among values of the code from 1 to 255, for instance, in case of expressing the value of the pixel data in an 8 bit.

Meanwhile, if the dark defect of the third pixel P₃ is discriminated only with the average value ‘α’, a serious problem is generated. For instance, the first pixel P₁ and the fifth pixel P₅ have the values of the codes, 129 and 131, respectively, thereby having the average value ‘α’, 130. At this time, if the value of the code of the third pixel P₃ is 131, the value of the code of the third pixel P₃, 131 is greater than the average value ‘α’ of the first pixel P₁ and the fifth pixel P₅, 130. Accordingly, it is concluded that the third pixel P₃ is the dark defect.

Furthermore, in an extreme way, if the dark defect of the third pixel P₃ is discriminated with ‘2α’ that is two times more than the average value ‘α’, the first pixel P₁ and the fifth pixel P₅ have the values of the codes, 59 and 61, respectively. Accordingly, ‘2α’ is 120. At this time, if the value of the code of the third pixel P₃ is 119, the average value ‘α’, 120 is greater than the value of the code of the third pixel P₃, 119, thereby concluding that the third pixel P₃ is not the dark defect.

However, these two embodiments described above are not enough to discriminate the dark defect.

Accordingly, in accordance with the present invention, to discriminate the dark defect more precisely, a threshold value (V_(T)) is used as a discriminating standard of the dark defect. Herein, the threshold value (V_(T)) is calculated by adding ‘α/n’ obtained by the average value ‘α’ divided by ‘n’ that is the multiple of 2, i.e., ‘α/2’ and ‘α/4’, to the average value ‘α’.

Accordingly, n is made to be selectively changed according to a low luminance of an image.

In case of that a value of ‘n’ is large, the threshold value (V_(T)) decreases. Thus, there is an advantage of more precisely detecting the dark defect. However, in this case, the concealment of the dark defect is more frequently generated, thereby inducing a deterioration of an image quality. Accordingly, it is preferable to decide the value of n selectively according to a luminance of the image.

FIG. 4 is a graph illustrating a dark defect discriminating region by using an average value ‘α’ and a threshold value ‘α+α/n’ in accordance with the present invention.

Referring to FIG. 4, the average value ‘α’ and two threshold values are exemplified. Herein, a first threshold value V_(T1) is calculated by ‘α+α/2’ and a second threshold value V_(T2) is calculated by ‘α+α/4’. In case of that the value of the code of the third pixel P₃ is an oblique lined region greater than either the first threshold value V_(T1) or the second threshold value V_(T2), it is concluded that the third pixel P₃ is the dark defect pixel and this dark defect is concealed. As for the concealment of the dark defect, a method for replacing the third pixel P₃ with the average value ‘α’ of the P₁ and the P₅ is used.

Subsequently, a threshold value applied to the present pixel is selected between the two threshold values V_(T1) and V_(T2) at step S103. Afterwards, the size of the value of the code is compared with the size of the threshold value of at step S104.

As a result of the comparison, if the value of the code of the corresponding pixel that is the third pixel P₃ is smaller than the threshold value of the third pixel P₃, the corresponding pixel that is the third pixel P₃ does not generate a dark defect. Accordingly, a dark defect concealment is omitted at step S106.

Meanwhile, if the value of the code of the third pixel P₃ is greater than the threshold value of the third pixel P₃, the corresponding pixel that is the third pixel P₃ is concluded as a pixel generating the dark defect for a moment.

FIG. 5 is a diagram illustrating an embodiment of detecting a dark defect within an installed window.

Referring to FIG. 5, the third pixel P₃ that is the pixel corresponding to detect the dark defect has an identical Bayer color with the first pixel P₁ and the fifth pixel P₅. The second pixel P₂ and the fourth pixel P₄ also have the identical Bayer color with each other.

Accordingly, {circle around (1)} denotes the average value α, {circle around (2)} denotes the threshold value ‘α+α/2’ and {circle around (3)} denotes the threshold value ‘α+α/4’.

At this time, when both of the first pixel P₁ and the fifth pixel P₅ have the value of the code, 10, the threshold value is 12.5 in case of using the threshold value calculated by {circle around (3)}. Accordingly, the value of the code of the third pixel P₃ is 15, thereby being greater than 12.5 that is the threshold value calculated by {circle around (3)}. Thus, in this case, it is concluded that the third pixel P₃ is the dark defect for a moment.

Meanwhile, if an edge exists in an actual image, situations become different.

That is, if the third pixel P₃ is concluded to be the dark defect as shown in FIG. 5, it may be possible that the edge actually exists in this portion, thereby changing the value of the code.

Accordingly, in case of that the value of the code of the corresponding pixel is greater than the threshold value, whether the edge exists or not within the window is judged at step S106.

FIG. 6 is a diagram illustrating an embodiment showing an edge existing within an installed window.

Referring to FIG. 6, if the first pixel P₁ and the fifth pixel P₅ have the values of the codes, 10 and 50, respectively and the third pixel P₃ has the value of the code, 50, the average value α becomes 30 due to the condition of (P₁+P₅)/2. If the threshold value corresponding to {circle around (3)} shown in FIG. 5 is applied, the threshold value is 5α/4, thereby becoming 37.5.

Accordingly, the value of the code of the third pixel P₃, 50 is greater than the threshold value, 37.5, the third pixel P₃ is concluded to be the dark defect. However, in case of this window, the edge exists in a region denoted with a dotted line so that the first pixel P₁ and the third pixel P₃ have the values of the codes having a big difference between them. In this case, if the concealment of the dark defect is performed after concluding the dark defect, the image quality is deteriorated. Thus, it is important to understand an existence of the edge with respect to the corresponding window.

For understanding the existence of the edge, an edge discriminating zone is set, thereby checking the existence of the edge by using this edge discriminating zone.

FIG. 7 is a diagram illustrating the edge discriminating zone.

In FIG. 7, a horizontal axis denotes the value of the code of the first pixel P₁ and a vertical axis denotes the value of the fifth pixel P₅ as for a method for expressing data in an 8 bit.

Referring to FIG. 7, a condition of P₄−P₂>(P₄+P₂)/2 is defined in a R₁′ region. If this condition is solved, a new condition of P₄>3P₂ is obtained. Also, a condition of P₂−P₄>(P₂+P₄)/2 is defined in a R1 region. If this condition is solved, a new condition of P₂>3P₄ is obtained. These two regions can be expressed with another condition of |P₂−P₄|>(P₄+P₂)/2.

That is, in the relationship between the second pixel P₂ and the fourth pixel P₄ adjacent to the third pixel P₃, one value of the code is three times greater than the other value of the code so that it is realized that the edge exists in this region.

Furthermore, a condition of P₅−P₁>(P₅+P₁)/4 is defined in a R₂′ region. If this condition is solved, a new condition of P₅>5/3P₁ is obtained. Also, a condition of P₁−P₅>(P₁+P₅)/4 is defined in a R₂ region. If this condition is solved, a new condition of P₁>3P₅ is obtained. These two regions can be expressed with another condition of |P₅−P₁|>(P₅+P₁)/4.

That is, in the relationship between the first pixel P₁ and the fifth pixel P₅ having the identical bayer color with the third pixel P₃, one value of the code is five thirds times greater than the other value of the code so that it is realized that the edge exists in this region. In case of that value of the code of the third pixel P₃ is falling under the four regions, R₁, R₁′, R₂ and R₂′, even though the value of the code of the third pixel P₃ exceeds the threshold value, the concealment of the dark defect is omitted at step S105.

Meanwhile, in case of a R₃ region that is not corresponding to the aforementioned four regions, since the edge does not exist in the corresponding window, the concealment of the dark defect is decided by a comparison between the value of the code of the third pixel P₃ and the threshold value.

That is, if the code value of the third pixel P₃ is greater than the threshold value and the edge does not exist, the third pixel P₃ is decided to be a defect pixel, thereby performing the concealment of the dark defect with respect to the third pixel P₃.

Meanwhile, in the image with an extremely low luminance, even though there is a little bit of difference in the values of the codes of the first pixel P₁, the second pixel P₂, the third pixel P₃, the fourth pixel P₄ and the fifth pixel P₅, it is judged as the edge, thereby not performing the concealment of the dark defect. As described above, a region where the values of the codes of both the first pixel P₁ and the fifth pixel P₅ are less than a predetermined value of the code is defined as a blocking zone, R₄ to prevent a region where the edge does not actually exist from being judged as the edge since the region where the edge does not actually exist satisfies with the condition of |P₂−P₄|>(P₂+P₄)/2 or |P₁−P₅|>(P₁+P₅)/2.

Accordingly, if the values of the codes of the first pixel P₁ and the fifth pixel P₅ are falling under the blocking zone, R₄, the concealment of the dark defect with respect to the third pixel P₃ is unconditionally performed.

At this time, in case of that a maximum critical value of the blocking zone, R₄ ranges from approximately 7 to approximately 32 in case of that the method for expressing the data of the 8 bit is a 255 code.

FIGS. 8A and 8B are photographs of transmission electron microscopy (TEM) illustrating an image quality improvement in case of applying the concealment of the dark defect in accordance with the present invention.

FIG. 8A illustrates a photograph before the image quality improvement, thereby observing a plurality of defects such as ‘X’ in the image. However, FIG. 8B illustrates a photograph after the image quality improvement, thereby observing that the defects are almost removed.

Meanwhile, in accordance with the embodiment of the present invention, although the pixel data comprised of the format of a red color, a green color and a blue color are exemplified, a format of complementary colors such as a yellow color, a magenta color and a cyan color can be applied.

The present invention performed as described above forms a window with a size of 1×5 by using a simple hardware constitution such as a shift resistor for sequentially outputting image pixel data. At this time, an average value and a threshold value are determined by using pixels having an identical color with a corresponding pixel in each window and then, a dark defect is judged by comparing the average value and the threshold value. Thus, a concealment of the dark defect is selectively performed, thereby judging an existence of an edge by using values of the adjacent pixels having the identical color and not having the identical color during judging the dark defect. In case of that the values of the pixels having the identical color within the window are less than a predetermined value, a blocking zone is set and thus, it is possible to improve an image quality by increasing precision during judging the dark defect and discriminating the edge.

The present invention provides an effect of improving an image quality of image data of an image sensor by minimizing a deterioration of the image through a concealment of a dark defect.

The present application contains subject matter related to the Korean patent application No. KR 2004-0029070, filed in the Korean Patent Office on Apr. 27, 2004, the entire contents of which being incorporated herein by reference.

While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. 

1. A method for concealing a dark defect in an image sensor, comprising the steps of: setting a window including five sequential pixels, a first pixel P₁, a second pixel P₂, a third pixel P₃, a fourth P₄ and a fifth pixel P₅, from a plurality of pixel data sequentially outputted, the third pixel and the fifth pixels P₃ and P₅ being identical in Bayer color with each other and the second and the fourth pixels P₂ and P₄ being identical in Bayer color with each other; calculating an average value ‘α’ of the first and the fifth pixels P₁ and P₅ and a plurality of ‘α/n’ obtained by dividing the average value ‘α’ by ‘n’, ‘n’ being a multiple of 2; selecting one of the plurality of ‘α/n’; comparing a threshold value ‘α+α/n’ calculated by adding the average value ‘α’ to the selected ‘α/n’ with a value of the third pixel P₃ in size; and omitting a concealment of the dark defect in the image sensor when the threshold value ‘α+α/n’ is greater than the value of the third pixel P₃.
 2. The method of claim 1, wherein further including a step of judging whether the edge exists or not within the window by the comparison result.
 3. The method of claim 2, wherein in the step of judging the edge, the concealment of the dark defect is omitted when the comparison result represents the existence of the edge within the window.
 4. The method of claim 3, wherein if one of conditions of |P₂−P₄|>(P₂+P₄)/2 and |P₁−P₅|>(P₁+P₅)/4 is satisfied, it is judged that the edge exists within the window.
 5. The method of claim 4, wherein even though the edge exists within the window by satisfying one of the conditions of |P₂−P₄|>(P₂+P₄)/2 and |P₁−P₅|>(P₁+P₅)/4, as the values of the first and the fifth pixels P₁ and P₅ are falling under a blocking zone having a less value than a predetermined value, the concealment of the dark defect is performed.
 6. The method of claim 5, wherein the predetermined value ranges from approximately 7 to approximately 32 in case of a 255 code of an 8 bit.
 7. The method of claim 1, wherein at the step of selecting one of the plurality of ‘α/n’, a detecting capability of the dark defect increases and an image quality degrades as a value of ‘n’ increases.
 8. The method of claim 1, wherein the pixel data is comprised of a format of a red color (R), a green color (G) and a blue color (B).
 9. A method for concealing a dark defect in an image sensor, comprising the steps of: extracting a window including five sequential pixels, a first pixel P₁, a second pixel P₂, a third pixel P₃, a fourth P₄ and a fifth pixel P₅, from a plurality of pixel data sequentially outputted, the third and the fifth pixels P₃ and P₅ being identical in Bayer color with each other and the second and the fourth pixels P₂ and P₄ being identical Bayer color with each other; calculating an average value ‘α’ of the first and the fifth pixels P₁ and P₅ and a plurality of ‘α/n’ obtained by dividing the average value ‘α’ by ‘n’, ‘n’ being a multiple of 2; selecting one of the plurality of ‘α/n’; comparing a threshold value ‘α+α/n’ calculated by adding the average value ‘α’ to the selected ‘α/n’ with a value of the third pixel P₃ in size; judging an existence of an edge within the window by using the comparison result; and performing the concealment of the dark defect in the image sensor when the comparison result is affirmative.
 10. The method of claim 9, wherein in the step of judging the existence of the edge in the window, the concealment of the dark defect with respect to the third pixel P₃ is performed as both of the first and the fifth pixels P₁ and P₅ are falling under a blocking zone having a value less than a predetermined value even though the edge exists in the window by satisfying one of conditions of |P₂−P₄|>(P₂+P₄)/2 and |P₁−P₅|>(P₁+P₅)/4.
 11. The method of claim 10, wherein the predetermined value ranges from approximately 7 to approximately 32 in case of a 255 code of an 8 bit.
 12. The method of claim 9, wherein at the step of selecting one of the plurality of ‘α/n’, a detecting capability of the dark defect increases and an image quality degrades as a value of n increases.
 13. The method of claim 9, wherein the pixel data is comprised of a format of a red color (R), a green color (G) and a blue color (B).
 14. A method for correcting pixel data in an image sensor, the method comprising: calculating a first threshold and a second threshold; determining a luminance value of an image from the image sensor, wherein the image comprises a first pixel having a first pixel value, a second pixel having a second pixel value, and a third pixel having a third pixel value; selecting one of the first threshold and the second threshold to form a selected threshold according to the luminance value; and concealing a dark defect in the image sensor if the second pixel value is greater than the selected threshold.
 15. The method of claim 14, further comprising: judging an existence of an edge in the window; and omitting the step of concealing a dark defect if the edge exists.
 16. The method of claim 14, wherein each of the first threshold and the second threshold are proportional to an average value of the first pixel value and the third pixel value.
 17. The method of claim 14, wherein the first pixel and the second pixel are separated by a pixel having a different color; and wherein the second pixel and the third pixel are separated by another pixel having a different color.
 18. A method for correcting pixel data in an image sensor, the method comprising: calculating a first threshold and a second threshold; wherein the first threshold and the second threshold are each proportional to an average value of a first pixel value and a third pixel value; selecting one of the first threshold and the second threshold to form a selected threshold; and concealing a dark defect in the image sensor if a second pixel value is greater than the selected threshold; wherein each of the first pixel value, the second pixel value, and the third pixel value are representative of a first color.
 19. The method of claim 18, further comprising: determining a luminance of an image comprising the first pixel value, the second pixel value, and the third pixel value; and wherein the step of selecting one of the first threshold and the second threshold is performed according to the luminance. 